The production of non-ferrous metals such as copper and nickel from concentrate occurs usually in the first stage pyrometallurgically. The processing of the copper matte formed in the first stage of treatment is generally continued further pyrometallurgically until the product is a cast copper anode, with a Cu content of 99.9%, which is routed to electrolytic refining to produce pure cathode copper. The fabrication of copper products starts with the smelting of a cathode, after which the molten copper can be cast in the desired shape and further processing depends on the goods to be produced. Further processing of the nickel matte generated in pyrometallurgical treatment is usually hydrometallurgical treatment. In this case nickel matte is ground, leached, solution purification is performed on the solution and finally the aqueous solution of nickel is routed to electrolytic recovery in order to form pure cathode nickel. Cobalt minerals often appear in the same ore as nickel minerals, particularly sulphides, and thus their production method is largely the same. The final product is often metallic cobalt in cathode form.
The final product of the metal production methods described above is a metal in cathode form. However, often some form other than a plate-like cathode would be more practical for the further processing of the metal.
An oxidation-reduction method for copper powder production is known in the prior art, for instance as described in JP patent application 2002327289, whereby an aqueous solution of sulphuric acid, which contains titanium, is routed to an electrolysis tank. The electrolysis anode is made of pure copper and there is a diaphragm between the anode and cathode. The electrolyte is routed from the cathode into the anode chamber whereupon the trivalent titanium of the cathode solution reduces the copper in the solution into metal powder, which precipitates in the anode chamber and is recovered from the solution.
US patent application 2005/0023151 (Phelps Dodge) describes a method for producing copper, in which exploitation of the ferrous/ferric anodic reaction is combined with conventional electrolytic copper recovery from a copper sulphate solution. According to the method, the solution entering electrolysis contains divalent iron in addition to divalent copper. In this case the cathodic reaction is the reduction of copper into metal and the anodic reaction is the oxidation of divalent iron to trivalent (ferrous/ferric). The ferric iron is regenerated by means of SO2 into ferrous iron and routed back to electrolysis. Since sulphuric acid is formed in regeneration, it must be neutralised from the solution. In the method copper is produced as a conventional cathode, but a further development of the method is described in US patent application 2006/0016684, where a flow-through cell is used as the electrolysis cell and copper is produced as a powder. When, in addition to conventional electrolysis, the redox potential achieved from the different degrees of oxidation of iron is used in the methods, the energy consumption is lower than in conventional EW electrolysis. In addition, the formation of acid mist is less.
There are some weaknesses in the methods described above. A method described in the Japanese publication 2002327289, whereby pure copper is used to produce Cu powder, results in the traditional impractical factors, e.g. anode scrap problems, electrolysis contact problems and the fact that Cu powder has numerous generation points, causing sensitivity to quality defects and control difficulties.
The electrolytic recovery of copper by utilizing the ferrous/ferric reactions of the anode also gives rise to various problems: Despite the fact that the vast majority of the Cu powder comes off the cathode, at least a small part remains attached, whereupon the cathode section will become clogged causing serious process interruptions. On a slightly larger scale there are dozens or hundreds of powder generation points, which leads to costly investments and high operating costs (maintenance costs). It is hard to control the quality of the metal powder regarding grain size and morphology, and there are also difficulties in attaining uniform quality in different cells. The SO2 used in the process is a problem and risk factor in work hygiene. In order for powder to be generated, a fairly high current density is required and this almost always leads to purity problems in metal powder. In addition, the separation of Cu powder from different cells is laborious.